The diesel engine is an internal combustion engine that uses compression ignition, in which fuel ignites as it is injected into air in a combustion chamber. More specifically, in a diesel engine, air is drawn into the cylinders and is compressed by the cylinder pistons. Near the end of the compression stroke, diesel fuel is injected into the combustion chamber. The fuel ignites from contact with the air, which due to compression has been heated to a temperature of about 1300-1650° F. The resulting combustion causes increased heat and expansion in the cylinder, which increases pressure in the cylinder and moves the piston downward. A connecting rod transmits this motion to a crankshaft to convert linear motion to rotary motion for use as power in a variety of applications.
Intake air to the engine is usually controlled by mechanical valves in the cylinder head. For increased power output, most modern diesel engines have a turbocharger, and some have a supercharger to increase intake air volume. Use of an aftercooler/intercooler to cool intake air that has been compressed, and thus heated, by the turbocharger increases the density of the air and leads to power and efficiency improvements.
Today's conventional diesel engine control systems are “fuel based”. An engine control unit determines the quantity of fuel to inject. Downward action of the throttle pedal causes the engine control unit to inject more fuel.
Typical fuel based engine control methods do not result in combustion that is sensitive to in-cylinder conditions. In particular, the combustion is not sensitive to airflow mass, air fuel ratio, or exhaust gas recirculation (EGR) rate. For some modern diesel engines, fuel injection is adjusted based on airflow mass measurement to control soot in small regions of the operating range, but this control method is still primarily fuel-based.